This invention relates generally to distance sensing devices and, more particularly, to a proximity ordnance fuze.
Prior art ordnance proximity fuzes have been devised which transmit a signal to a reflecting target surface and analyze the time difference between the transmitted and received echo signals to provide an indication of the distance between the ordnance vehicle in which the fuze is located and the target. These prior art ordnance fuzes have worked relatively satisfactorily where the reflecting target surface is a rigid, hard surface, such as ground level or the like, but have been somewhat unsatisfactory where the reflecting surface is not the actual target. Thus, for example, where the ordance fuze is located in any aerial ordnance vehicle, such as, for example, a bomb or a projectile, and where ground level is the target against which it is desired to detonate the vehicle a predetermined burst height distance above, but the target is covered by an intervening media, such as a foliage canopy or the like, the transmitted signal will be reflected by the foliage canopy rather than by the ground target thereby yielding a burst height which is referenced to the foliage canopy rather than the level of the ground target. Such action considerably reduces the lethality of the ordnance vehicle.
Systems have been devised which attempt to accurately obtain the desired burst height distance with reference to the target rather than with reference to intervening media, such as foliage or the like. One such system utilized in aerial ordnance devices, such as bombs or projectiles, senses the foliage canopy and, rather than immediately detonating the bomb which would provide a burst height with reference to the foliage canopy, delays detonation a predetermined time to allow the ordnance device to more closely approach the intended target to obtain an approximate burst height with reference to the target. This system, however, has proven less than satisfactory since the foliage canopies are not always of uniform height which results in improperly chosen time delays and, consequently, inaccurate and ineffective burst heights. Similarly, this system is unsatisfactory where the ordnance fuze senses the desired target, for example, through a clearing to the foliage or the like, but is preset with a predetermined time delay resulting, therefore, in an unwarranted detonation delay and consequent less lethal or ineffective detonation.
Furthermore, prior art ordnance fuzes are prone to premature detonation or the like by RF fields. These RF fields may result from stray RF signals or may be part of a complex countermeasure technique directed at the fuze. Conventional ordnance fuzes are not able to be adequately shielded from RF fields since these fuzes require at least some opening in the ordnance device in which they are located for transmitting a signal to a target and for receiving the echo signal therefrom.